The AKG K-3003 is at least close to a landmark Universal IEM, in my view. Pricey, yes, but one of the first Universals to aspire to the heights that the best of the Custon IEM's aspire to. They are well built (though some may not like the idea of non-detachable cables) and attractive enough. But the real issue is, of course, the sound, so let's get right to it.
The first thing that hit me about the AKG's is that they invite comparison to full size phones in certain ways more that other IEM's. The combination of excellent coherency top to bottom, excellent but not hyped detail and resolution, low distortion, good dynamics and relative neutrality show up even good IEM's such as the Sony MDR-EX1000, Audio Technica CK-10, Ortofon EQ-7 and the like as pretenders. Let's take some of these features forward for further scrutiny.
These sound quite consistant as a solo instrument (piano, violin, guitar etc.) is played up and down the key/fret board. Lesser IEM's will tend to, worse case, sound uneven in amplitude or, less destructively, thin or fatten the harmonic envelope (this is where our ability to discern instruments of different model/construction comes from) under these conditions. A good example of this is the album The Virtuoso Guitar as played by Alirio Diaz on a Vangard recording. If the guitar doesn't sound like the same guitar through its range, the illusion of an expert musician playing his instrument is damaged. This coherency pays off even further during the Castelnuevo-Tedesco Guitar Concerto #1 off this album where the interplay between soloist and orchestra is preserved.
The high linearity (low distortion) of the 3003 allows one to hear deep into the lower levels of recordings without the masking effects of distortion products. This allows low level information to be heard in the mix of popular music or orchestral presentation. This allows things like the "humming along" Ivan Moravec provides in his VAI label Beethoven recordings (original on Connoisseur Society) or the various sonic manipulations on the Beatles "Strawberry Fields" to be heard clearly for what they are. This detail is not the "thrown in your face" detail of certain treble emphasized phones but is an organic part of the recording not obscured by transducer playback artifacts.
This is where the 3003 really excells over lesser IEM's. The combination of lack of low level artifacts and high (for IEM's) level linearity makes for a wide dynamic envelope. The Fritz Reiner RCA recording of "Isle of the Dead" (off "The Reiner Sound" album) is a great example of this. This recording starts very much hushed (as befits a piece called Isle of the Dead) but swells to quite loud crescendos. The AKG's can accomodate this without distortion (beyond the slight tape saturation on the highest peaks endemic to the otherwise excellent late '50 recording) or without compromising the soundfield by coagulating the instruments together, quite a feat for an IEM. Careful, don't listen too loud! The low distortion and high levels attainable can lead to this...
I use this term because I am not sure what absolute neutrality would be. Neutral to the recording? Neutral to the original sound of the original performace? Neutral to some preconsceived idea how a phone "should" measure? Neutral to the your personal preference? Or some combination?
The AKG tends to be neutral to the recording, which tends to result in a somewhat front-of-the-hall perspective. Still neutral to the original performace, but some may like a bit of a more distant perspective as personal preference. One of my tests for the "gestalt" of the concert hall is the EMI recording of the Barbirolli Mahler 9 with the Berliner Philharmoniker. This is a good, but somewhat forward, recording of an excellent performance of this evocative piece. If the playback puts you into the hall without putting the forwardness "over the top", it's good playback. The 3003 does this, to be sure.
For further evaluation, let's go to the classics. I personally use Iggy and the Stooges "Search and Destroy". This is a recording made with the VU meters pegged, as it should be! An IEM that can deliver the swagger, threat and excitement of this is doing it justice and the AKG does it justice, in my view. A particular favorite group of mine is the sound world of The Legendary Pink Dots. The combination of the Silverman's swirling keyboards and Edward Ka-Spel's wispy lyrics and vocals (inside joke) make for music that can take you to some less-visited places inside. The fact that I can be sitting on the train on the way home from work and still escape to the Dots' world is as good a recommendation as I can give.
Bottom line. Between AKG, Final Audio Design and various of the custom designers the IEM has been brought into higher levels of performance than ever before. Here in the States, one has to give credit to Ultimate Ears and JH Audio for pioneering the idea that custom IEM's can aspire to greatness and that audiophiles would respond to the performance by paying the price. And now we can thank AKG and Final Audio Design for believing that those of us who don't want customs would also pay for high performance.
Some will balk at the 5 star rating for value. The K3003 are indeed not cheap, but I know of no way currently to get equivalent performance in a universal IEM at a lesser price. To me, that's priceless.